Noise Intensity Level and Duration of Exposure

The risk of noise to hearing is based upon two factors: noise
intensity level (loudness) and the duration of exposure.
Noise induced hearing loss has been found to occur with repeated 8
hour exposures of 85 dBA, but shorter exposures to greater levels can
be equally as dangerous.

The chart below identifies equivalent noise exposures. Based upon the
equal energy law, a doubling of sound energy will result in a 3 dB increase
in measured sound level. This 3 dB exchange rate is the recommended
method for evaluating the risk of noise exposure. OSHA action levels
(which trigger required inclusion in a hearing conservation program)
are based upon a 5 dB exchange rate.

Noise Intensity Time Exchange

Length of
Exposure

NIOSH
(3 dB
Exchange Rate)

OSHA
(5 dB
Exchange Rate)

16 hours

82

80

8 hours

85

85

4 hours

88

90

2 hours

91

95

1 hour

94

100

30 min

97

105

15 min

100

110

7.5 min

103

115

3.75 min

106

120

Examples:

For determining risk, a 4 hour exposure to 88 dBA is equal
to an 8 hour exposure to 85 dBA (3 dB exchange).

For purposes of OSHA compliance, a 4 hour 90 dBA exposure is equivalent
to the required action level of 85 dBA Time Weighted Average (TWA).